A conventional method and device are described, for example, in International Patent No. WO 95/14595, which describes a hydraulic vehicle braking system operated by an external force. The system is equipped with valves that can be controlled to enter into intermediate positions by a corresponding flow control system using a control device. In this context, the pressure at the wheel brakes is sensed and compared with the pressure at a main brake pressure transmitter, and the valves are controlled in such a way that the pressure set at the main brake pressure transmitter is regulated. However, detailed information regarding the controller to be used in the control unit is not provided in this prior art.
German Patent Application No. 196 54 427.0 of Dec. 24, 1996 (not previously published) describes a pressure controller for the pressure in at least one wheel brake. The valve current that is outputted from this controller to regulate the pressure buildup and pressure reduction is composed of a controlled component, which is derived from stored valve characteristic curves, and a correction component which is formed from the control deviation between the reference and actual pressures. The valve characteristic curve for pressure buildup and pressure reduction contains the information, necessary for regulation, as to which differential pressure is established at the valve for the respective activation current. It has been found that these characteristic curves, which define the operating point of the pressure controller for pressure buildup and pressure reduction, must be determined with a high degree of accuracy in order to achieve an adequate control quality. And, manufacturing tolerances and aging processes in the valves have a substantial detrimental influence on the accuracy of the characteristic curves.